Method of and device for pre-refining highly carburized metallic melts



United States Patent 1 2,856,280 METHOD OF AND DEVICE FOR PRE-REFINING HIGHLY CARBURIZED METALLIC MELTS Ludwig A. von Bogdandy, Essen-Frintrop, Germany, as-

signor to Hiittenwerk Oberhausen Aktiengesellschaft, Oberhausen, Germany No Drawing. Application July 8, 1955 Serial No. 520,901 Claims priority, application Germany July 26, 1954 3 Claims. (Cl. 75-60) The present invention relates to a method of prerefining highly carburized melts such as pig iron melts, by means of a blast rich in oxygen.

It is known that in connection with various steel making processes it is highly advantageous to subject the pig iron prior to the refining process proper to a treatment which will increase the temperature of the melt and will vary its composition, for instance by reducing the contents in silicon. Ever since oxygen has been available in greater quantities and at low prices for metallurgical processes, the above mentioned. method, known as pro-refining, has gained increased importance inasmuch as it has been found that the desired effects can be particularly economically obtained by means of refining means rich in oxygen. However, the pre-refining method with oxygen has the great disadvantage that, when blowing in the refining means rich in oxygen, considerable quantities of a rather bothersome brown smoke forms which consists of very fine grained dust, the major portion of the dust particles having a diameter below mu. To remove such fine dust particles from the flue requires considerable technical equipment.

In order to save the high costs of such complicated dust removal installations, attempts have been made to prevent such dust accumulation at the very place where the dust originates, i. e. at the highly overheated surface where the refining means hits the bath. To this extent, steam has been added to the refining means. This method, however, is disadvantageous insofar as by the addition of water, a considerable portion of the heat developed during the pro-refining process is lost again whereby the efficiency of the method is greatly affected, i. e. impaired.

It .is, therefore, an object of the present invention to provide a method of pre-refining highly carburized melts such as pig iron, by means of oxygen or an oxygen-enriched blast, which will have the beneficial efiect inherent to such pre-refining method without having the drawbacks heretofore encountered with such pre-refining method.

It is another object of this invention to provide a method of pre-refining a highly carburized metallic melt as set forth in the preceding paragraph, which will prevent the formation of the highly bothersome brown smoke encountered heretofore in connection with such method.

It is a further object of this invention to provide a vessel for use in connection with the pre-refining of a metallic melt by means of oxygen or oxygen-enriched refining means, which will make it possible to carry out such pre-refining without encountering the drawbacks heretofore inherent to such pre-refining method.

It has been found in connection with the present invention that the development of dust in connection with the oxygen pre-refining of highly carburized melts such as pig iron will take place only when during the prerefining process carbon is caused to burn. It is assumed that this phenomenon is due to the fact that the CO- bubbles formed during the oxidation of the carbon act as carriers for the Fe-vapors. While this explanation is a mere assumption, numerous tests carried out in this connection appear to bear out this theory. The term "ice oxygen pre-refining covers both the employment of pure oxygen as well as an oxygen-enriched. refining means and the claims attached hereto are to be read with this interpretation.

In order to avoid the accumulation of dust in the melt when pro-refining highly carburized melts with oxygen or oxygen-enriched pro-refining means, it is suggested, according to the present invention, to effect the prerefining operation in a vessel covered with a smooth surface coat of slag. This coat or layer should be such that in the presence of CO it will be wetted incompletely only.

Tests have proved that when employing such a vessel for pre-refining highly carburized melts with oxygen or oxygen-enriched pre-refining means the development of dust is reduced almost completely. In connection therewith it has also been found that the obtained effect is practically independent of the chemical composition of the coating on the inner surface of the melt-containing vessel. It is merely important that the glazing covers the entire inner surface of said vessel and that said coating in spite of its thinness-a coating of 0.1 millimeter will sufiice already-will wear only slowly. Particularly favorable results have been obtained with a coating representing a slag coating of the following composition:

4.4% Fe 3.4% Mn 14.5% Cr 37.6% SiO This slag film was effective with pig iron melts up to 1600 C. and was satisfactorily resistant against fines.

The coating of the inner wall of the pig iron ladle with a slag film is preferably effected by spraying but may also be obtained by coating the walls with a suspension of the respective slag powder with water or another binding means or by melting such slag film upon the walls of the vessel. The glazing process can then be carried out by burning by means of any convenient burner.

The method according to the present. invention has proved, when refining basic iron, automatically to produce an earlier de'phosphorization.

It is, of course, understood that the present invention is, by no means, limited to the particular example of the slag composition set forth in the specification but also comprises any modifications within the scope of the appended claims.

What I claim is:

1. A vessel for use in connection with oxygen prerefining of a metallic melt, characterized in that said vessel is lined with a smooth surface slag coating covering the entire inner surface of said vessel and adapted in the presence of CO to be wetted incompletely only.

2. A vessel for use in connection with oxygen prerefining of a metallic melt, characterized in that said vessel is lined with a glazed smooth surface slag coating comprising 4.4% Fe, 3.4% Mn, 14.5% Cr, and 37.6% of SiO 3. A method of pre-refining a highly carburized metallic melt in a vessel, which includes the steps of: depositing a film of slag upon the surface of the interior of said vessel, subsequently glazing said film, to form a slag coating adapted in the presence of CO to be wetted incompletely only, and to prevent the formation of brown smoke, pouring the melt to be refined into the thus glazed interior of said vessel, and blowing oxygen enriched refining means into the melt in said vessel.

References Cited in the file of this patent UNITED STATES PATENTS 225,932 Jones -e Mar. 30, 1880 302,088 Beasley July 15, 1884 499,248 Reese June 13, 1893 

3. A METHOD OF PRE-REFINING A HIGHLY CARBUIZD METALLIC MELT IN A VESSEL, WHICH INCLUDES THE STEPS OF:DEPOSITING A FILM OF SLAG UPON THE SURFACE OF THE INTERIOR OF SAID VESSEL, SUBSEQUENTLY GLAZING SAID FILM, TO FOR A SLAG COATING ADAPTING IN THE PRESENCE OF CO TO BE WETTED INCOMPLETELY ONLY, AND TO PREVENT THE FORMATION FO BROWN SMOKE, POURING THE MELT TO BE FINED INTO THE THUS GLAZED INTERIOR OF SAID VESSEL, AND BLOWING OXYGEN ENRICHED REFINING MEANS INTO THE MELT IN SAID VESSEL. 